Predictive control for slip and breakthrough determination of selective catalytic reduction systems

Abstract

Disclosed are SCR predictive control systems, methods for using such control systems, and motor vehicles with SCR employing predictive control. A method for regulating operation of an SCR system includes receiving sensor signals indicative of NOx output downstream from an SCR catalyst, and sensor signals indicative of exhaust gas temperature upstream from the SCR catalyst. The method determines if a model error condition has occurred for the NOx output signal and, responsive to such an occurrence, modulating dosing injector output for at least a calibrated designated time period. Upon expiration of the designated time period, the dosing injector is activated and commanded to inject reductant in accordance with a modulated dosing value. After the dosing injector injects the modulated dosing value of reductant, the method determines if the SCR system is underdosing or overdosing based on a response shape of signals received from the outlet NOx content sensor.

What is claimed: 
     
       1. A predictive control system for regulating a selective catalytic reduction (SCR) system, the SCR system including an SCR catalyst, a reductant storage tank fluidly connected to the SCR catalyst, and a dosing injector for injecting reductant onto the SCR catalyst to chemically reduce nitrogen oxide (NOx) emissions, the predictive control system comprising:
 an outlet NOx content sensor configured to detect NOx output downstream from the SCR catalyst and output signals indicative thereof; 
 an inlet SCR temperature sensor configured to detect exhaust gas inlet temperature upstream from the SCR catalyst and output signals indicative thereof; and 
 an electronic control unit (ECU) communicatively connected to the outlet NOx content sensor and the inlet SCR temperature sensor, the ECU being configured to:
 receive, from the outlet NOx content sensor, a signal indicative of the NOx output downstream from the SCR catalyst; 
 receive, from the inlet SCR temperature sensor, a signal indicative of the exhaust gas inlet temperature upstream from the SCR catalyst; 
 determine if a model error condition has occurred for the NOx output signal; 
 responsive to a determination that the model error condition has occurred, determine a designated time period based on the exhaust gas inlet temperature signal; 
 command the dosing injector to modulate output for at least the designated time period; 
 determine a modulated dosing value for the dosing injector; 
 upon expiration of the designated time period, command the dosing injector to activate and inject reductant in accordance with the modulated dosing value; and 
 determine if the SCR system is in an underdose state or an overdose state based on a response shape of signals received from the outlet NOx content sensor after the dosing injector is commanded to inject the modulated dosing value of reductant. 
 
 
     
     
       2. The predictive control system of  claim 1 , wherein the ECU is further configured to, responsive to a determination that the SCR system is in the underdose state, increase a commanded injection value of the dosing injector. 
     
     
       3. The predictive control system of  claim 1 , wherein the ECU is further configured to, responsive to a determination that the SCR system is in the overdose state, decrease a commanded injection value of the dosing injector. 
     
     
       4. The predictive control system of  claim 1 , further comprising:
 an inlet NOx content sensor configured to detect NOx input upstream from the SCR catalyst and output signals indicative thereof; 
 an outlet SCR temperature sensor configured to detect exhaust gas outlet temperature downstream from the SCR catalyst and output signals indicative thereof, 
 wherein determining the designated time period is further based on an NOx input signal received from the inlet NOx content sensor and an exhaust gas outlet temperature signal received from the outlet SCR temperature sensor. 
 
     
     
       5. The predictive control system of  claim 1 , further comprising:
 an SCR catalyst temperature sensor configured to detect current temperature of the SCR catalyst and output signals indicative thereof, 
 wherein determining a designated time period is further based on a calibrated ammonia burn-off mass determined based on a current temperature signal received from the SCR catalyst temperature sensor. 
 
     
     
       6. The predictive control system of  claim 1 , further comprising a memory device communicatively connected to the ECU and storing an SCR chemical model calibrated for the SCR system. 
     
     
       7. The predictive control system of  claim 6 , wherein determining if the model error condition has occurred includes identifying a model value from the SCR chemical model for a current SCR system operating condition, and determining if the NOx output signal is greater than or less than the model value by a system calibrated value. 
     
     
       8. The predictive control system of  claim 1 , wherein determining the SCR system is in the underdose state includes the response shape of the signals received from the outlet NOx content sensor including a substantially large negative slope. 
     
     
       9. The predictive control system of  claim 1 , wherein determining the SCR system is in the underdose state includes the response shape of the signals received from the outlet NOx content sensor including a substantially large relative change between beginning and end values. 
     
     
       10. The predictive control system of  claim 1 , wherein determining the SCR system is in the overdose state includes the response shape of the signals received from the outlet NOx content sensor including a substantially zero slope. 
     
     
       11. The predictive control system of  claim 1 , wherein the ECU is further configured to determine if the SCR system is in a steady state condition, and wherein the determining if the model error condition has occurred is responsive to a determination that the SCR system is in a steady state condition. 
     
     
       12. The predictive control system of  claim 11 , further comprising:
 an inlet NOx content sensor configured to detect NOx input upstream from the SCR catalyst and output signals indicative thereof, 
 wherein determining if the SCR system is in the steady state condition includes calculating a root mean square of NOx input signals received from the inlet NOx content sensor. 
 
     
     
       13. The predictive control system of  claim 1 , wherein determining the modulated dosing value includes determining a commanded injection value for a current SCR system operating condition, and multiplying the commanded injection value by an injection calibration value. 
     
     
       14. A motor vehicle, comprising:
 a vehicle body defining an engine compartment; 
 an internal combustion engine (ICE) assembly stowed in the engine compartment, the ICE assembly including an engine block with a plurality of cylinders bores, and a plurality of pistons each reciprocally movable within a respective one of the cylinder bores; 
 a selective catalytic reduction (SCR) system fluidly coupled to the ICE assembly, the SCR system including an SCR catalyst, a storage tank storing a fluid reductant and fluidly connected to the SCR catalyst, and a dosing injector operable to inject the fluid reductant from the storage tank to the SCR catalyst; 
 an outlet NOx content sensor configured to detect NOx output downstream from the SCR catalyst and output signals indicative thereof; 
 an inlet SCR temperature sensor configured to detect exhaust gas inlet temperature upstream from the SCR catalyst and output signals indicative thereof; and 
 a programmable electronic control unit (ECU) communicatively connected to the outlet NOx content sensor and the inlet SCR temperature sensor, the ECU being programmed to:
 receive, via the outlet NOx content sensor, a signal indicative of the NOx output downstream from the SCR catalyst; 
 receive, via the inlet SCR temperature sensor, a signal indicative of the exhaust gas inlet temperature upstream from the SCR catalyst; 
 determine if a model error condition has occurred for the NOx output signal; 
 responsive to a determination that the model error condition has occurred, determine a designated time period based on the exhaust gas inlet temperature signal; 
 command the dosing injector to modulate output for at least the designated time period; 
 determine a modulated dosing value for the dosing injector; 
 upon expiration of the designated time period, command the dosing injector to activate and inject reductant in accordance with the modulated dosing value; and 
 determine if the SCR system is in an underdose state or an overdose state based on a response shape of signals received from the outlet NOx content sensor after the dosing injector is commanded to inject the modulated dosing value of reductant. 
 
 
     
     
       15. A method of operating a predictive control system for regulating a selective catalytic reduction (SCR) system, the SCR system including an SCR catalyst, a reductant storage tank fluidly connected to the SCR catalyst, and a dosing injector for injecting reductant onto the SCR catalyst to chemically reduce nitrogen oxide (NOx) emissions, the method comprising:
 receiving, via a controller from an outlet NOx content sensor, a signal indicative of an NOx output downstream from the SCR catalyst; 
 receiving, via the controller from an inlet SCR temperature sensor, a signal indicative of an exhaust gas inlet temperature upstream from the SCR catalyst; 
 determining if a model error condition has occurred for the NOx output signal; 
 responsive to a determination that the model error condition has occurred, determining a designated time period based on the exhaust gas inlet temperature signal; 
 modulating output of the dosing injector for at least the designated time period; 
 determining a modulated dosing value for the dosing injector; 
 upon expiration of the designated time period, activating and commanding the dosing injector to inject reductant in accordance with the modulated dosing value; and 
 after the dosing injector is commanded to inject the modulated dosing value of reductant, determining if the SCR system is in an underdose state or an overdose state based on a response shape of signals received from the outlet NOx content sensor. 
 
     
     
       16. The method of  claim 15 , further comprising:
 responsive to a determination that the SCR system is in the underdose state, increasing a commanded injection value of the dosing injector; and 
 responsive to a determination that the SCR system is in the overdose state, decreasing a commanded injection value of the dosing injector. 
 
     
     
       17. The method of  claim 15 , wherein determining the designated time period is further based on an NOx input signal received from an inlet NOx content sensor and an exhaust gas outlet temperature signal received from an outlet SCR temperature sensor. 
     
     
       18. The method of  claim 15 , wherein determining a designated time period is further based on a calibrated ammonia burn-off mass determined based on a current temperature signal received from an SCR catalyst temperature sensor. 
     
     
       19. The method of  claim 15 , wherein determining if the model error condition has occurred includes identifying a model value for a current SCR system operating condition from an SCR chemical model calibrated for the SCR system, and determining if the NOx output signal is greater than or less than the model value by a system calibrated value. 
     
     
       20. The method of  claim 15 , wherein determining the SCR system is in the underdose state includes the response shape of the signals received from the outlet NOx content sensor including a substantially large negative slope, and wherein determining the SCR system is in the overdose state includes the response shape of the signals received from the outlet NOx content sensor including a substantially zero slope.